Experiment of the Formation of Adiabatic Shear band in Sheet Metal ABSTRACT

Transcription

1 Experiment of the Formation of Adiabatic Shear band in Sheet Metal Jiho Lim, Woojong Kang, Hoon Huh ABSTRACT The adiabatic shear band formation is one of the high speed deformation phenomena, in which adiabatic shear failure is physically observed as a narrow band of the continuous shear strain In this paper, the experiment of the formation of the adiabatic shear band in sheet metal is carried out for high strength steel sheets, and In order to carry out experiments with a tension split Hopkinson bar, shear specimens are designed to induce large shear strains The shear deformation of the two sheet metals of and is quite different and the adiabatic shear band is observed with only The width of a shear band is measured by comparison of the hardness in a crack tip The shear deformation in is restrained and the crack is propagated by a tensile mode since the strain hardening of in the high strain rate is large The load-displacement curves show that the load with becomes higher than that with as the displacement increases : Shear Band( ), Hopkinson Bar( ), TRIP (thermal softening) (localization) (adiabatic shear band) 1)

2 Zener Hollomon 2) bar) (tension split Hopkinson Fig 1 Schematic description of the tension split Hopkinson bar TRIP (transformation induced plasticity), micro-vickers -, 4,5) S 1 S 2, (1) Kolsky (2) E, A 0, A C 0, L 3) Fig 1,

3 245m/s 200kPa Fig 2 Schematic description of a shear specimen nital (etching) Fig 2 L 6mm D 02mm, 04mm, 06mm, -08mm micro-vickers mm 2mm, C-Mn-Si TRIP (transformation induced plasticity) TRIP - 600MPa Fig 3 Deformed shapes of a shear specimen of at D=04mm when displacement is 385mm D 02mm,04mm,06mm Fig 3 D=04mm 385mm

4 Fig 4 Optical micro of shear specimen of at D=04mm when displacement is 385mm Fig 4, D=04mm Fig 6 Optical micro of shear specimen of at D=-08mm when displacement is 325mm 4~5 Fig 6 Fig 5 Deformed shapes of a shear specimen of at D=-08mm when displacement is 325mm Hardness (HV) Distance from the center(µ m) Fig 5 D=-08mm 325mm D=04mm D=04mm Fig 6 D=-08mm, Fig 7 Hardness in front of the crack of shear specimen of at D=-08mm when displacement is 325mm Fig 7 D=-08mm 100~ HV 400

5 HV Fig 6 D=-08mm 150 D Fig 8 (a) (b) Fig 8 Deformed shape of a shear specimen of 60 TRIP at D= -08mm Fig 9 Optical micrograph of shear specimen of 60 TRIP at D=-08mm: (a) I; (b) II; (c) III Fig 9 Fig9(a) Fig 9(b) Fig 9(d) Fig 10-2mm - 15mm -

6 Load per unit depth (kn/mm) ~16mm, D=04mm, D=-08mm, D=04mm, D=-08mm Displacement (mm) Fig 10 Comparison of load-displacement curves of and - D 02mm, 04mm, 06mm 04mm Fig 10, 6mm 02mm, 04mm, 06mm, -08mm 02mm, 04mm, 06mm -08mm mm 1 M A Meyers, Dynamic Behavior of Materials, John Wiley & Sons, New York, C Zener and J H Hollomon, Effect of Strain Rate upon Plastic Flow of Steel, J Appl Phys, Vol15, pp22-32, J A Jukas, T Nicholas, H F Swift, L B Greszczuk, and D R Curran, Impact Dynamics, John Wiley & Sons, New York, ,,,, " Tension Split Hopkinson Bar," A, Vol 21, No 12, pp , W J Kang, S S Cho, H Huh and D T Chung, "Identification of Dynamic Behavior of Sheet Metals for an Autobody with Tension Split Hopkinson Bar," SAE Int Congress, Detroit, USA, 1998